Alarm system



J. SCHULEIN Nov. 12, 1968 ALARM SYSTEM 2 Sheets-Sheet 1 Filed Aug. 2. 1965 INVENTOR JOSEPH SCHULEIN ATTORNEY J. SCHULEIN ALARM SYSTEM Nov. 12, 1968 2 Sheets-Sheet 2 Filed Aug. 2, 1965 INVENTOR JOSEPH SCHULEIN ATTORNEY United States Patent 3,411,150 ALARM SYSTEM Joseph Schulein, P.0. Box 1825, Vancouver, Wash. 98663 Filed Aug. 2, 1965, Ser. No. 476,248 3 Claims. (Cl. 340-216) ABSTRACT OF THE DISCLOSURE An alarm system for indicating when the plug of an electrical appliance has been disconnected from an electrical outlet which is supplied electrical power from a pair of supply conductors. The system includes a switch in the outlet which is closed upon removal of the plug, and a transmitter also contained within the outlet which is energized on closing of the switch, and which on being energized transmits an electrical signal from a pair of output terminals to respective supply conductors. A receiver remote from the transmitter is connected to the supply conductors to receive such a signal.

This invention relates to an alarm system, and more particularly to an alarm system which will give an alarm when electrically powered apparatus, such as an appliance, is disconnected from its source of power.

In places like hotels and motels where television sets, radios, etc. are provided in the rooms, theft of such equipment is a recurrent problem. Without some kind of protective alarm system, an owner or manager of an establishment normally has no way of monitoring various rooms, and thus finds it extremely difficult to prevent theft.

Known alarm systems for protecting against theft of electrical equipment usually require extensive special wiring in a building, and as a consequence are relatively difficult and costly to install. With such systems also the extra wiring required is often easily noted enabling any would-be thief to detect the presence of the alarm system. With such notice, a thief may be able successfully to deactivate the system.

The alarm system contemplated by the present invention avoids the problems attending these known systems, and at the same time provides reliable protection.

A general object of this invention is to provide an improved alarm system for signaling when equipment such as an appliance is disconnected from the usual supply conductors that supply power to the equipment.

Another object is to provide an alarm system which will indicate positively whenever a plug and socket type connection is broken.

Yet another object of the invention is to provide an alarm system which may easily and rapidly be installed in a completed building.

A further object is to provide a plug-operated alarm system which is reliable and economical in operation.

Still another general object is the provision of an alarm system which readily enables the monitoring of a plurality of electrical outlets.

Another object is the provision of a system where alarm-producing signals are transmitted over power supply conductors which are connected to an outlet, thereby obviating the need for special wiring.

More specifically, an object of the invention is to provide an alarm system as described, which employs a transmitter and a receiver, where the transmitter is operat-ively connected adjacent an electrical outlet to elec- 3,411,150 Patented Nov. 12, 1968 "ice trical supply conductors, and is adapted to transmit an alarm-producing signal over the conductors to a receiver which is remote from the transmitter, whenever a plug or other fitting is removed from the outlet.

These and other objects and advantages of the invention will become more readily apparent when the description which follows is read in conjunction with the appended drawings, wherein:

FIG. 1 is a schematic diagram partly in block form, illustrating an alarm system constructed according to the invention;

FIG. 2 is a circuit diagram of a transmitter employed in the alarm system of FIG. 1; and

FIG. 3 is a circuit diagram of a receiver used in the alarm system of FIG. 1.

Turning now to the drawings, and with reference first to FIG. 1, shown generally at 10 is an alarm system as contemplated. In the system illustrated, 12 indicates an electrical socket-type outlet, of the type that might be mounted on the wall of a building, and at 14 and 16 are shown the usual line conductors that supply conventional AC power to the outlet.

The outlet includes a pair of terminals 18 and 20, each having a pair of spaced-apart conductive elements A and B electrically connected together. The terminals are joined to the line conductors by conductors 22 and 24. Each terminal is constructed to be able to receive one of the prongs of an ordinary electrical plug or outlet fitting of the type usually provided in a television set, radio or other electrical appliance.

The outlet further includes switch mechanism 26 comprising a moveable arm 26a and a fixed contact 26b which the arm normally engages in the absence of any plug inserted into the outlet. The arm is electrically connected to element A of terminal 20, and on a plug being inserted into the outlet, the arm is shifted to the position indicated in dashed lines, where it is spaced from contact 26b.

A transmitter 30 represented in block form in FIG. 1 is suitably mounted within the housing, or outlet box for the outlet. Conductor 32 connects the transmitter directly to element B of terminal 18, and conductor 34 connects the transmitter to contact 2612 of the switch mechanism. It is in this manner that with the switch mechanism closed, the transmitter draws power from the line conductors through terminals 18 and 20. On drawing power, the transmitter transmits an electrical signal (as will be more fully explained) through conductors 32 and 34 to the line conductors.

The alarm system also includes a receiver 36 shown as a block in FIG. 1. The receiver is connected by conductors 38 and 40 to the line conductors at a location remote from the outlet and transmitter, and receives a signal fed into the line conductors by the transmitter.

An electrical appliance, such as a television set, is shown at 42. Connecting the set to the outlet is an electrical plug 44 and a power cable 46. The plug includes the usual prongs 48 and 50, which are received in terminals 18 and 20 with the set connected to receive power from the line conductors.

Turning now to FIG. 2 for a more detailed description of the transmitter, this unit comprises multiple stages including a DC power supply 52, an audio oscillator 54, an audio amplifier 56, a modulator 58 and a carrier oscillator 60.

The DC power supply is connected by conductors, or power supply terminals, 62 and 64 to conductors 32 and 34, respectively, and through these conductors it draws AC power from the terminals in the outlet. Power supply 52 produces a DC voltage (with the polarity indicated in the drawings) at a pair of power output terminals 66 and 68. DC power is supplied to the transmitter from terminals 66 and 68 by conductors 7 0, 72.

The audio oscillator in the transmitter employs a unijunction transistor 74 having an emitter 76 and a pair of bases 78 and 80. Base 78 is connected to conductor 72 through a resistor 82, and base 80 is connected to conductor 70 through a resistor 84. Bias voltage is supplied emitter 76 through a variable resistor 86 which is connected between the emitter and conductor 70. The emitter is connected also to conductor 72 through a charging capacitor 88. The unijunction transistor functions in a well-known manner as a relaxation oscillator producing, in the present circuit, oscillations having a predetermined audio frequency. Output signals from the oscillator are fed from emitter 76 to audio amplifier 56 by a coupling resistor 90.

The audio amplifier comprises a transistor 92 including an emitter 92e, a base 92b and a collector 92c. Signals from the oscillator are fed to the base of the transistor through resistor 90. The collector is connected directly to conductor 70, and the emitter is supplied with bias voltage from conductor 72 through a biasing resistor 94. Output signals from the amplifier are provided at the emitter of the transistor.

Turning next to modulator 58, it comprises a modulating transistor 96 having an emitter 962, a base 96b and a collector 96c. Bias voltage for the base is provided by a pair of biasing resistors 98 and 100, with resistor 98 being connected between the base and conductor 70 and resistor 100 being connected between the base and conductor 72. Signals are supplied to the base of the modulating transistor from the emitter of transistor 92 by a coupling circuit comprising a resistor 102 and a capacitor 104. The emitter of the modulating transistor is connected directly to conductor 72, and the collector is connected through a choke 106 to conductor 70. The collector is also connected to conductor 72 through a conductor 108 and a capacitor 110. The modulator further comprises a protective diode 112 with the cathode of the diode being connected to conductor 70 and the anode being connected through a conductor 114 and conductor 108 to the collector of the modulating transistor. The diode protects the modulating transistor against sudden voltage surges across the transistor.

The carrier oscillator comprises a transistor 116 having an emitter 116e, a base 116b and a collector 1160. The transistor forms part of a tuned-collector oscillator circuit. Supply voltage for the carrier oscillator is provided by conductor 72, and a conductor 118 which is connected at a junction 120 between conductor 114 and the anode of diode 112. Bias voltage for the base of transistor 116 is developed at a bias node 122 between a pair of biasing resistors 124 and 126 which are connected between the node and conductors 118 and 72, respectively. A by-pass capacitor 128 is connected between the node and conductor 72 in parallel with resistor 126. This bias voltage is supplied to the base of transistor 116 by a tickler coil 130. The emitter of the transistor is connected directly to conductor 72 and the collector is connected to conductor 118 through the parallel combinations of a tuning capacitor 132 and a winding 134a of a variable output transformer 134. The tickler coil is used as a feed-back device between the collector and base in the transistor, and is preferably positioned closely adjacent the transformer winding 134a. The carrier-oscillator, when powered, oscillates at a carrier frequency determined by the tuning of transformer-134 and capacitor 132. In the preferred embodiment illustrated, a carrier frequency of about 300 kilocyclcs per second has been found to work satisfactorily.

Explaining briefiy how this carrier frequency is modulated by the modulator to produce an output electrical signal, when an audio signal is applied to the base of transistor 96 in the modulator, the collector voltage of the transistor varies in proportion to amplitude variations in the applied voltage. This collector voltage is used, in turn, to supply bias voltage to carrier oscillator 60, wherein variations in the supply voltage cause corresponding variations in the amplitude of output signals produced in the oscillator. This has the effect of modulat ing the amplitude of signals produced in the carrier oscillator.

Another winding 134b of transformer 134 is employed as an output winding and is connected through a pair of capacitors 136 and 138, and a pair of conductors, or signal output terminals, 140 and 142, to conductors 32 and 34, respectively. Electrical signals produced on supplying power to the transmitter are fed through conductors 32, 34, terminals 18, 20, and conductors 22, 24 to the power conductors. Thus, it will be noted that switch 26 together with conductors 32, 34 constitute a circuit connecting both terminals 62, 64, and terminals 140, 142, to the power conductors.

Turning now to FIG. 3 wherein the receiver is illustrated in detail, it includes DC power supplies 144 and 146, a pair of carrier amplifiers 148 and 150 connected in cascade, a demodulator circuit 152, an audio amplifier 154 and an alarm signal indicator 156.

AC power from conductors 38 and 40 is fed to supplies 144 and 146 by conductors 158, 160, 162, and 164 as shown. Supply 144 is adapted to provide DC voltage to the various amplifiers in the receiver through a conductor 166, and supply 146 is adapted to provide DC voltage to the alarm signal indicator through a conductor 168.

The receiver includes an input circuit for feeding signals from conductors 38 and 40 to carrier amplifier 148. This input circuit comprises a variable input transformer having a primary winding 170a and a secondary winding 170b, a pair of input capacitors 172 and 174 connecting the primary winding to conductors 38 and 40 as shown, a tuning capacitor 176 connected in parallel with the secondary winding, and a coupling capacitor 178. The input transformer and tuning capacitor are tuned to the carrier frequency of transmitter 30.

Capacitor 178 in the input circuit is connected to the grid of a pentode vacuum tube 180 in amplifier 148. The suppressor and cathode electrodes in the tube are con nected together by a conductor 182, and are connected to ground through a variable resistor 184. The screen electrode is bypassed to ground through a capacitor 188, and is supplied with bias voltage by a resistor 186. The plate and screen electrodes are connected together through a tuning circuit which comprises a variable capacitor connected in parallel with a variable choke 192, and this tuning circuit is tuned to the carrier frequency of transmitter 30. Bias voltage for the plate in tube 180 is provided by a resistor 186 and choke 192 which are connected in series between the plate and conductor 166.

Amplified output signals from amplifier 148 are fed from the plate of tube 180 by a coupling capacitor 194 to the grid of a pentode vacuum tube 196 in carrier amplifier 150. The suppressor and cathode electrodes in tube 196 are connected together by a conductor 198, and are connected to ground through a variable resistor 200. The screen electrode is bypassed to ground through a capacitor 202, and is provided with bias voltage by a pair of biasing resistors 204 and 206, with resistor 204 connected between the screen and conductor 166, and with resistor 206 connected between the screen and ground. The plate and screen electrodes in tube 196 are connected together through the parallel combination of a capacitor 208 and a winding 210a of a variable transformer 210. Plate bias voltage is provided by a resistor 204 and transformer winding 210a which connect the plate to conductor 166. Transformer 210 is tuned with capacitor 208 to the carrier frequency of transmitter 30.

Considering now the demodulator circuit, it comprises a diode detector 212 and a filtering network connected to the diode including a resistor 214 and a capacitor 216 connected in parallel with each other, and a resistor 218 and capacitor 220 connected in series with each other across capacitor 216. Signals are fed to the demodulator from amplifier 150 by a winding 21% in transformer 210. Winding 210b is connected as shown to the diode detector and resistor 214. The demodulator operates to detect the envelope of signals coming to it from amplifier 150.

The receiver includes a feed-back circuit connected between the demodulator and amplifiers 148 and 150. This circuit comprises a potentiometer 222 having a winding 222a which is connected between capacitor 216 and ground, as illustrated, and a wiper 222b which is connected to the grids of tube 180 and 196 through resistors 224 and 226, respectively.

Considering now audio amplifier 154, it comprises a pentode vacuum tube 230. The suppressor and cathode electrodes in the tube are connected together by a conductor 232 and are connected to ground through a conductor 234. The grid electrode is connected to ground through a resistor 236, and is coupled to the demodulator circuit by a coupling capacitor 238 through which it receives signals from the demodulator. Bias voltage is provided for the screen electrode by a biasing resistor 240 which is connected between the screen and conductor 166, and bias voltage is supplied to the plate electrode through a coil 242a which forms part of a resonant relay 242. The relay further includes an arm 242b and a contact 2420 which are normally open and are shown spaced apart in the drawing. Contact 2420 is connected to ground through a conductor 244, and arm 242b is connected by a conductor 246 to the alarm signal indicator (yet to be discussed). The relay responds to a current of predetermined frequency flowing through its coil to actuate arm 242b, whereupon the arm closes with contact 2420. The predetermined frequency here is selected to be the same as the frequency of audio oscillator 54 in the transmitter. Thus, when a signal is received from transmitter 30, the arm and contact in relay 242 will close.

Turning now to the alarm signal indicator, it comprises a transistor 248 having an emitter E, a base B and a collector C. The emitter is connected directly to ground, as shown, and the base and collector are connected to ground through capacitors 250 and 252, respectively. Bias voltage for the base is provided by a resistor 254 which is connected between the base and conductor 168, and bias voltage for the collector is provided through a coil 256a of a relay 256. Relay 256 includes an arm 256b and a contact 2560 which are normally closed, as illustrated. The arm is connected to conductor 168 by a conductor 258, and the contact is connected to ground through an indicator lamp 260. The base of the transistor is connected by conductor 246 to the arm in relay 242.

With relay 242 nonenergized, and with bias voltage supplied to the base and collector of transistor 248, the transistor will conduct and will energize relay 256, whereupon arm 256b will separate from contact 256a. When relay 242 energizes and causes arm 242b to close with contact 2420, the base of transistor 248 will be connected to ground through a circuit including conductor 246, arm 242b, contact 2420, and conductor 244, and this will cause the transistor to cease conducting, whereupon relay 256 will be deenergized. When this happens, arm 256b will close with contact 2560 and will thereby complete a circuit supplying power to lamp 260, this circuit including power supply 146, conductor 168, conductor 258, arm 256b, contact 2560, lamp 260, and ground.

Explaining now the operation of the alarm system as a whole, and assuming that plug 44 is plugged into outlet 12, in the preferred embodiment of the invention arm 26a in the switch mechanism will then be shifted to a position where it is out of engagement with contact 26b. With this condition, power is cut off from the transmitter. Should the plug be removed from the outlet (as would be done if a thief were to remove set 42), arm 26a closes against contact 26b and completes a circuit to supply power to the transmitter, this circuit comprising power conductor 14, conductor 22, terminal 18, conductor 32, transmitter 30, conductor 34, closed switch mechanism 26, terminal 20, conductor 24 and power conductor 16.

On power flowing to the transmitter, the transmitter produces an electrical signal modulated in amplitude at the frequency of oscillations produced by audio oscillator 54, and this signal is fed by capacitors 136 and 138 to the power conductors for transmission. The electrical signal which is supplied to the power conductors may be called an alarm-producing signal, and, in the preferred embodiment now being discussed, is transmitted over the power conductors each time the transmitter is supplied with power.

The electrical signal transmitted over the power conductors is received in the receiver through input capacitors 172 and 174, and is demodulated therein to detect the audio signal which was used for modulating. This audio signal is then amplified in amplifier 154 and fed to relay 242 where, when it has the appropriate frequency, it actuates arm 242b thus to close the arm with contact 2420.

On closing of the the arm and contact in relay 242, transistor 248 ceases to conduct, as was explained earlier, whereupon relay 256 deenergizes. When this happens, arm 256a closes with contact 256b and completes the circuit described above which supplies power to the indicator lamp. Thus, the lamp lights up upon removal of plug 44 from the outlet, giving a positive indication that the appliance has been disconnected.

It will be apparent from the foregoing description that the transmitter and receiver are relatively easy to construct, and that the transmitter may readily be made into a compact unit which will fit conveniently into existing electrical outlets. Moreover, it will be apparent that the system is relatively inexpensive to construct, since it requires no special transmission wiring, employing instead the existing power wiring in a building.

The system can easily be expanded so that it will monitor a large number of outlets, simply by employing a separate transmitter in each outlet, with each transmitter using a different modulating frequency, and by including additional resonant relays and alarm indicators in the receiver to correspond to each modulating frequency.

Other modifications are possible, such as employing switch mechanism in an outlet whereby the transmitter is turned off rather than on when a plug is removed from the outlet. In such a modification, an alarm-producing signal would be transmitted over the power conductors on turning 011 of a transmitter.

Further variations and modifications may become apparent to those skilled in the art and will be possible without departing from the basic principles of the invention, and it is desired to cover all such variations and modifications which come within the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. An alarm system for indicating when the plug of an electrical appliance is detached from an outlet supplied electrical power through a pair of supply conductors comprising a transmitter for transmitting an alarm signal with a pair of input power supply terminals and a pair of signal output terminals,

a circuit for connecting the power supply terminals to said suply conductors and for connecting the signal output terminals to said supply conductors,

said circuit including switch means which actuates to place the transmitter -in operative transmitting condition with its signal transmitted into said supply conductors when the plug of the appliance is detached from the outlet, and

receiving means electrically coupled to said supply conductors at a point remote from said transmitter 7 8 adapted to receive an alarm signal transmitted by References Cited said transmitter and to producean alarm therefrom. UNITED STATES PATENTS 2. The system of claim 1, wherein said switch means comprises a switch that closes to complete the circuit 2,637,020 4/1953 Stegall 3403 10 X between said supply conductor and said power supply 5 3,045,226 7/1962 lf 340280 terminals upon detachment of the plug and outlet, 3,127,597 3/1964 Lewln et a1 whereby said transmitter is energized on closing of said 3,234,543 2/1966 Thompson et 340 310 X switch, with the transmitter drawing power from said Supply conductors JOHN W. CALDWELL, Primary Exammer.

3. The system of claim 1, wherein said transmitter is 10 D, L, TRAFION, As istant Ex min r contained within outlet. 

